In this article, our Cook County trust dispute attorneys explain undue influence in trust litigation. Undue influence is a cause of action used to invalidate a trust based on a third party taking some wrongful, illegal, or fraudulent action to deprive the grantor of the trust of his or her free will, thereby subverting his or her actual wishes. Undue influence is much easier to prove if the alleged wrongdoer was a trusted fiduciary of the grantor of the trust.